This invention relates to stacking rings used to support periodic groups of fairing segments for towed marine systems for sonar, communication, mine sweeping and oceanographic exploration which are normally deployed into the sea and tethered to a moving vessel at speeds ranging from 0 to 50 knots. Quite often when velocities exceed 10 knots, it is necessary to add streamlined fairings to the entire length of tow cable in order to reduce cable strumming (cable vibration) and in order to increase system depth performance by reducing the cable drag.
Performance problems with fairings can occur due to fluid drag force components which act parallel to the cable axis. This axial force is cumulative and can create a force of several thousand pounds on the bottom fairing. Not only can this stacking force crush fairings at the bottom, but also it can cause jamming and distortion of the fairing shape which prevents the fairing from rotating freely in the flow, resulting in poor performance.
The solution to the problem is to fasten a suspension device which transfers the load to the cable at intervals (typically 5-10 feet) down the cable length, instead of allowing the force in each fairing to accumulate, and at the bottom of the cable, to jam the fairings.
Prior solutions have incorporated hard metallic rings which are installed either by compression techniques on pretensioned cables, or by welding the ring seam shut with clearance between the cable, and vulcanizing rubber between the ring and cable to form a bond. Generally the process requires various forms of welding, brazing, cable pretensioning, special tooling and individual testing because of the elasticity and compressibility of tow cables.
Metallic rings have numerous deficiencies: Hard nodes or rings produce concentrated regions of stress which reduce the fatigue life of the cable; metallic rings attached to the cable are larger than the cable and generally slightly larger than the fairing diameter, and passage of the ring through sheaves and winding on storage drums under tension can cause damage to the sheaves and drums; metallic rings are not field-installable or repairable; metallic rings corrode in the sea water/marine environment, and some forms actually accelerate corrosion of the cable itself; metallic rings present poor bearing surfaces for the fairing; metallic rings are relatively expensive; and metallic rings cannot readily adapt to cable diameter changes which occur as a result of cable tensioning and postforming of the cable during use.